1. Field of the Invention
This invention relates generally to inflatable packers for use in wellbores, and specifically to inflatable packers, which have an elastomeric cover disposed over an annular inflatable wall.
2. Description of the Prior Art
In the drilling and production of oil and gas wells, it is frequently necessary to isolate one subterranean region from another and prevent the passage of fluids between those regions. Conventional packers and bridge plugs are used as packing devices in wellbores containing fluid for providing a seal between a conduit which carries the device downward in the wellbore and an interior surface within the wellbore, such as casing or an uncased wellbore wall.
One type of double anchor, packing device includes two regions of expandable material which serve to grip the interior surface within the wellbore. Usually, an elastomeric annular cover is provided between the two anchor regions. The elastomeric annular cover also radially expands outward, and eventually engages the desired surface and forms a seal, thus preventing the passage of fluid.
When a packing device having a small diameter is lowered in a wellbore for engaging and forming a seal with a much larger diameter casing, the elastomeric annular cover is subjected to extraordinary multi-dimensional strain, including bi-axial and tri-axial strain, that is, a strain having two or three dimensional components. Consequently, it is possible for the outer flexible cover to split, destroying the utility of the packing device.
"Soft set" is another frequently encountered problem in the prior art devices. Soft set occurs when fluid is trapped between each end of the outer cover of the packing device. When a soft set occurs, the packing device is not as firmly anchored as possible, and may slip or rotate unexpectedly.